1. Field of the Invention
The present invention pertains to a method for disposing of solid wastes by forming a slurry which is injected into a hydraulically fractured earth formation in a zone which includes alternate formation layers of relatively low permeability and relatively high permeability.
2. Background
Certain types of solid waste material may be permanently disposed of by reducing the particle size of the solid material, forming a slurry with a carrier liquid and injecting the material into a subterranean earth formation. U.S. Pat. No. 5,109,933 issued May 5, 1992 to James E. Jackson and assigned to the assignee of the present invention describes a system and method for disposing of the cuttings formed during the drilling of an oil well and the like. Other types of solid waste which may be ground into relatively fine particle sizes and slurried with a carrier liquid, such as water, may also be disposed of in the manner generally in accordance with the '933 patent. However, the amount of slurried waste which may be injected into a subterranean earth formation is dependent upon several factors including the compressive stress in the earth at the zone of injection, the permeability of the earth formation and the composition of the slurry. In this regard certain problems arise which are solved by the method of the present invention.
Hydraulic fracturing of earth formations to stimulate production of hydrocarbon fluids from subterranean formations has been carried out in many parts of the world over the past 40 years or more. In hydraulic fracturing to stimulate the production of fluids, the injection fluid which forms the hydraulic fracture is commonly provided with a fluid loss control agent to minimize the leakage of fluid into the formation from the opposed faces of the fracture so that the fracture extension pressure may be maintained to obtain the desired fracture length and height. Conversely, in disposing of fluidized waste material into an earth formation, leak-off of the carrier fluid is desired so that a greater quantity of slurry may be injected into a disposal zone. However, if the permeability of the formation zone in which the fracture is being formed is relatively high, a layer of solids particles or so-called "filtercake" will rapidly accumulate on the faces of the fracture which will reduce the flowpath for the disposal slurry and result in increased pumping pressure. Control over pumping pressure must be maintained to prevent vertical or other uncontrolled growth of the fracture which may break into a zone in the earth formation which will provide an undesired flowpath for the waste material such as into a water supply area or other fluid-producing area of the formation.
Accordingly, it has been discovered that certain formation characteristics of a disposal zone for injecting solid wastes should be present so that the capacity of a particular disposal well to hold the disposed wastes in the desired zone is not unduly limited by the interference to fluid flow. The present invention overcomes certain of these problems by providing a method for disposing of solid wastes in a subterranean formation which will accommodate an increased volume of waste material from a particular disposal well without the risk of extending the fracture out of the disposal zone of interest. Accordingly, the invention results in reduced costs for disposing of solid wastes in subterranean earth formations and minimizes the risk of uncontrolled flow of the waste material into zones other than a desired waste disposal zone.